1. Field of the Invention
The present invention relates to a decorative sheet and a method of making the decorative sheet and also relates to a decorated formed product and a method of making such a product.
2. Description of the Related Art
Recently, it was disclosed that a decorative sheet could be attached to the surface of a formed product as a technique for decorating various types of formed products. A formed product with a decorative sheet can be recycled more easily than a formed product with a painted surface. In addition, a decorated product can have a different type of aesthetic appearance from that of a painted product.
FIG. 12 illustrates a typical decorative sheet. The decorative sheet 210 shown in FIG. 12 includes a base member 201 made of a resin material such as polycarbonate or polyethylene terephthalate and an ink layer 202 arranged on the principal surface 201a of the base member 201. By attaching this decorative sheet 210 to the surface of a formed product 221 in the order shown in FIGS. 13A, 13B and 13C after an adhesive layer 203 has been applied onto the ink layer 202, a formed product 220 with a decorated surface (which will be referred to herein as a “decorated formed product”) can be obtained.
The formed product 221 shown in FIG. 13A includes a hemispherical (cuplike) raised portion 221a and therefore has a rugged, three-dimensional surface. For that reason, the decorative sheet 210 being attached is stretched so as to follow the rugged surface perfectly. To stretch the decorative sheet 210 to follow the rugged surface perfectly, the decorative sheet 210 is typically heated and softened before being attached.
FIG. 14 schematically illustrates a vacuum/compressed air forming system 200 for making a decorated formed product 220 such as the one shown in FIG. 13C. The vacuum/compressed air forming system 200 includes a gripping frame 230 to grip the decorative sheet 210 thereon, a supporting stage 231 for supporting a formed product thereon, heaters 233 for heating the decorative sheet 210, and a vacuum vessel 234 that houses all of these members.
The vacuum vessel 234 consists of a main vessel 234a that houses the gripping frame 230 and the supporting stage 231, and a sub-vessel 234b that houses the heaters 233. When the decorative sheet 210 is heated, the heaters 233 are introduced into the main vessel 234a.
The supporting stage 231 has a plurality of openings 231a through which the air inside the main vessel 234a can be exhausted. Although not shown in FIG. 14, a mechanism for introducing a gas from outside of this system into the main vessel 234a is also provided for the main vessel 234a.
Using this vacuum/compressed air forming system 200, a decorated formed product may be made as shown in FIGS. 15 through 17.
First, as shown in FIG. 15A, a formed product 221 is mounted on the supporting stage 231 and a decorative sheet 210 is fixed onto the gripping frame 230. As partially enlarged in FIG. 15A, an adhesive layer 203 has been applied onto the ink layer 202 of the decorative sheet 210.
Next, as shown in FIG. 15B, the decorative sheet 210 is heated with the heaters 233. In this process step, the decorative sheet 210 is preferably heated to such a temperature that enables the base member 201 to stretch easily and also enables the adhesive layer 203 to exhibit sufficiently strong adhesion.
Thereafter, as shown in FIG. 16A, the decorative sheet 210 is brought down toward the formed product 221 and then the pressure in the space 235 between the decorative sheet 210 and the formed product 221 is reduced while the pressure in the space 236 above the decorative sheet 210 is increased, thereby bonding the decorative sheet 210 onto the formed product 221 as shown in FIG. 16B.
Subsequently, as shown in FIG. 17A, an excess portion 210a of the decorative sheet 210 is trimmed with a rotating blade or any other cutter, and then the formed product 221 is removed from the supporting stage 231, thereby completing a decorated formed product 220 as shown in FIG. 17B. By performing such a vacuum/compressed air forming process, even a formed product with a rugged surface can be decorated easily and beautifully.
Recently, various sorts of synthetic leathers that feel soft and smooth and look rich and impressive have been disclosed as interior materials for cars. For example, Japanese Patent Application Laid-Open Publication No. 2000-303365 discloses suede-leather-looking, non-woven fabric with good stretchability as a type of synthetic leather.
The present inventors tentatively used this type of fabric, which is a different material from the conventional decorative sheets, in the vacuum/compressed air forming process. As a result, the present inventors discovered that in the process step of reducing and raising the pressures as shown in FIG. 16A, the air permeated through the fabric to pull and tear a portion of the fabric or make the distribution of the adhesive locally uneven, thus destroying the beauty of its appearance.
Additionally, Japanese Patent Application Laid-Open Publication No. 52-78970 discloses a technique for performing a vacuum/compressed air forming process with an impermeable sheet stacked on a permeable sheet. According to such a technique, first, a formed product 321 mounted on a vacuum forming mold 331 has its surface coated with an adhesive 303 as shown in FIG. 18A. Next, as shown in FIG. 18B, a permeable sheet 310 (e.g., a resin sheet or woven fabric with micropores) is placed on the formed product 321. Thereafter, as shown in FIG. 18C, the formed product 321 and the permeable sheet 310 are covered with an impermeable sheet 340 such as a rubber film, and the pressure in the vacuum forming mold 331 is reduced to a state to thereby obtain a decorated formed product 320 as shown in FIG. 18D.
According to the technique disclosed in Japanese Patent Application Laid-Open Publication No. 52-78970, the pressure reducing process step is carried out with the permeable sheet 310 covered with the impermeable sheet 340, and therefore, it is possible to prevent the permeation of the air through the permeable sheet 310 from destroying the beauty of the appearance.
If the adhesive 303 were applied onto the surface of the formed product 321 as disclosed in Japanese Patent Application Laid-Open Publication No. 52-78970, however, the following problems would arise. Specifically, if the formed product 321 has a rugged surface, then the permeable sheet 310 needs to be bonded onto the formed product 321 while being stretched so as to follow that ruggedness. That is why if the degree of ruggedness is significant (e.g., to the point that the permeable sheet needs to be stretched so that portions of the permeable sheet bonded to the formed product 321 will be 30-70% as thick as the original thickness of the permeable sheet), then the molten adhesive 303 will flow so as to make the thickness of the adhesive 303 uneven. With the adhesive 303 having such an uneven thickness, the adhesion will be insufficient where the adhesive 303 is too thin, thus making it difficult to have the permeable sheet 310 bonded so as to follow the rugged surface of the formed product 321 perfectly. In other words, the permeable sheet 310 will have a decreased degree of formability. On the other hand, where the adhesive 303 is too thick, the adhesive 303 will penetrate through the surface of permeable sheet 310 (i.e., the surface opposite to the formed product 321), thus ruining the decorativeness (including the smooth feel and fine appearance) of the permeable sheet 310.
Japanese Patent Application Laid-Open Publication No. 52-78970 discloses that the adhesive 303 could be applied to the permeable sheet 310 but does not disclose at all exactly how to apply the adhesive 303 or how much adhesive 303 needs to be applied. The present inventors carried out extensive research on how a decorative sheet, including a permeable decoration layer such as a non-woven fabric, should be applied to the vacuum/compressed air forming process. As a result, the present inventors discovered that even when the adhesive was simply applied to such a permeable decoration layer, the same problems as those described above also happened and the desired high degrees of formability and decorativeness could not be achieved at the same time.